Liquid crystal devices include organic or inorganic orientating films which are made of, for example, polyimide or SiO, and which are formed on their surfaces of transparent substrates made of glass or the like. In a rubbing process performed before assembly of the liquid crystal devices, the surfaces of the orientating films are rubbed by a fibroid rubbing member in one direction, and thereby liquid molecules are orientated in a predetermined direction.
Japanese Patent Application, First Publication, No. Hei 3-126917 discloses a rubbing method as shown in FIGS. 4 and 5. Referring to FIG. 4, to make a positive visible angle consistent with a viewing angle, rubbing is performed obliquely with respect to a side of the substrate 1. In a conventional rubbing method, a rubbing roller 4 is moved down obliquely from upper onto a starting position 8 whose vertical position corresponds to that of the substrate 1 and whose horizontal position is separated from that of the substrate 1, and then starts rotation. The rubbing roller 4 is moved in a rubbing roller moving direction 9, rubbing the orientating film 2 of the substrate 1.
A rubbing cloth 3 starts to come in contact with a corner 6 of the substrate 1, at which point hairs of the rubbing cloth 3 may fall off, be cut off, or lie down, thereby making the hairs in contact with the corner 6 irregular. Orientating irregularities may thereby arise in an area rubbed by the irregular hairs 7, and display of the liquid crystal display may become irregular.
Referring FIG. 5, in order to avoid the irregularities of the orientation due to the irregular hairs caused by the contact between the rubbing cloth and the corner 6 of the substrate 1, the rubbing cloth 3 on the surface of the rubbing roller 4 starts to come in contact with, not the corner 6 of the substrate 1, but an inner portion of the corner 6 at the start.
That is, the rubbing roller 4 is moved down from upper to the inner portion of the corner when it starts rubbing, preventing the hairs of the rubbing cloth 3 from falling off, being cut off, and lying down when the rubbing cloth 3 comes in contact with the substrate 1 at the start.
However, there is a problem that a sufficient space is necessary between the corner 6 of the substrate 1 and a border of the orientating film because the rubbing roller 4 must be moved down therebetween. The space must be longer than a contact length of the rubbing cloth 3 against the substrate 1. When the length of the space is less than the contact length, the rubbing cloth 3 may come in contact with the corner 6 when the rubbing roller 4 is moved down, and the above effect cannot be achieved.
In general, the contact length of the rubbing cloth against the substrate is set in a range of approximately 10 to 20 mm. According to the method shown in FIG. 5, the orientating film cannot be applied to an area within 10 to 20 mm from the corner 6 of the substrate, and this reduces the display area of the liquid crystal display device, thus lowering production efficiency.
Japanese Patent Application, First Publication, No. Hei 6-95119 discloses a rubbing apparatus shown in FIG. 6. The apparatus has a switch 12 for starting and terminating an operation, and a measuring means 11 for measuring a vertical position of a surface of a substrate and converting the measured value into a quantity of electricity, which is output to a central processing unit 14.
The central processing unit 14 stores the measured value in a random-access memory 16. A read-only memory 15 beforehand stores the value of the gap between the substrate and the rubbing roller which is predetermined so as to obtain an appropriate pressure. A movement distance of a stage which is movable vertically is calculated based on these values. The stage is moved up or down by the movement distance by means of a stage vertical movement drive 18.
The stage is moved horizontally by means of a stage horizontal movement drive 17 so that the substrate approaches the rubbing roller. Then, the rubbing roller starts to rotate due to a roller rotator 13 and rubs the substrate with the appropriate rubbing pressure.
Referring to FIG. 7, a rubbing method disclosed in Japanese Patent Application, First Publication, No. Hei 5-323302 will be explained. Edges 45 and corners 44 of a substrate 1 of a liquid crystal display device are chamfered so as to have curved surfaces. This prevents hairs of a rubbing cloth from falling off, being cut off, and lying down when the rubbing cloth comes in contact with the substrate 1.
However, the number of liquid crystal display elements which can be produced from one substrate is reduced, and alternatively the size of the elements become small. This is because the liquid crystal elements are rectangular and an effective area from which the liquid crystal elements are produced is reduced through the chamfering process.
As described above, in the rubbing method shown in FIG. 4 there is a problem that a rubbing cloth comes in contact with a corner of the substrate, at which point hairs of the rubbing cloth may fall off, be cut off, or lie down, thereby making the hairs in contact with the corner 6 irregular. Orientating irregularity may thereby arise in an area rubbed by the irregular hairs 7, and the display of the liquid crystal display may become irregular.
In the rubbing method shown in FIG. 5, there is a problem that a sufficient space is necessary between the corner of the substrate and an end of the orientating film, and this reduces a display area of the liquid crystal display device, thus lowering productivity.
The technique shown in FIG. 6 prevents deficiency such as the orientating irregular due to irregularity in the rubbing pressure, because the rubbing is performed with the appropriate rubbing pressure by means of the measuring means 11. However, even when the technique is applied to the apparatus shown in FIG. 4, a rubbing cloth comes in contact with a corner 6 of the substrate, at which point hairs of the rubbing cloth may fall off, be cut off, or lie down, and the irregularity of the hairs in contact with the corner cannot be prevented, and thus display of the liquid crystal display may become irregular.